[n]peristylanes and [n]oxa[n]peristylanes (n = 3-6): A theoretical study

Theoretical studies at the HF and Becke3LYP levels using 6-31G* basis sets were carried out on a series of [n]peristylanes and [n]oxa[n]peristylanes ( n = 3-6) to understand their structure and energetics. The structures of th e [3]- and [4]peristylanes (1, 2) and their era-derivatives (5, 6) were cal culated to have the anticipated high symmetry, C-nv. In contrast, a C-s str ucture (9) at HF/6-31G* and another (25) at the Becke3LYP/6-31G* level were calculated for the [5]oxa[5]peristylane. The energy difference between the m is extremely small even though there are major differences in the structu res indicating every soft potential energy surface: On the other hand, the potential energy surface of [6]oxa[6]peristylane is not as soft. Similar st ructures were also calculated for the top rings. Calculations on the seco-c ompounds 11-14 and 15-19 (Table 4) indicate that there is no unusual strain involved in the formation of 27 from 19. The Li+ interaction energies of t he [n]oxa[n]peristylanes are 61.7 (n = 3), 72.8 (n = 4), 84.2 (n = 5) and 9 1.7 (n = 6) kcal mol(-1) at the Becke3LYP/6-3IG* level. Dramatic difference s between the C-C bond lengths obtained from the solid state X-ray diffract ion studies and those from the calculations for the [n]oxa[n]peristylanes w ere also observed.